There is an increasing demand for a high data rate in wireless communications. As techniques that fulfill such a demand, techniques, such as STBC (Space Time Block Code), OFDM (Orthogonal Frequency Division Multiplexing), and polarization diversity, have been proposed in the following documents.
[Non-patent document 1] A. V Zelst, R. V Nee and G. Awater, Space Division Multiplexing (SDM) for OFDM Systems, Proc. of VTC, pp. 15-18, 2000.
[Non-patent document 2] J. J. A. Lempianen, J. K. Laiho-Steffens, A. Wacker, Experimental results of cross polarization discrimination and signal correction values for a polarization diversity scheme, Proc. of VTC 97, vol. 3, pp. 1498-1502, 1997.
[Non-patent document 3] E. Shin and S. Safavi, A simple theoretical model for polarization diversity reception in wireless mobile environments, proc. of ISAP 99, vol. 2, pp. 1332-1335, 1999.
[Non-patent document 4] Chang-Jun AHN, Iwao Sasase, Convolutional Coded Coheretn and Differential Unitary Space-Time Modulated OFDM with Bit Interleaving for Multiple Antennas system, THE INSTITUTE OF ELECTRONICS, TECHNICAL REPORT OF IEICE, SST 2002-47, pp. 75-80, October 2002.[Non-patent document 5] S. M. Alamouti, A Simple transmit diversity scheme for wireless communication, IEEE Journal of Sel. Communication, Vol. 19, No. 1, pp. 48-60, January 2001.[Non-patent document 6] M. Rupp, C. F. Meeklenbrauker, On extended Alamouti Schemes for Space-Time Coding, Proc. of WPMC 2002, Vol. 1, pp. 115-118, October 2002.
Non-patent document 1 discloses an invention relating to the OFDM scheme. Particularly, it shows that the use of a plurality of antennas on both a receiver side and a transmitter side can achieve a high transfer rate on multiple input multiple output (MIMO) channels.
However, various schemes which can achieve faster communications with higher quality are further demanded.
Further, non-patent document 2 discloses a polarization diversity scheme. It is known the XPD (CROSS Polarization discrimination) value for a combination of a horizontal polarization antenna and a vertical polarization antenna varies between 5 dB and 15 dB depending on the environment.
This is the result of measuring the ratio of reception powers in orthogonal diversity branches. When the reception powers of the polarization branches become equal to each other, the maximum diversity gain is achieved.
When the unbalance of reception powers becomes large, however, the diversity gain is not achieved. This is because weak channels are neglected at the stage of coupling diversities.
Non-patent document 3 discloses an ideal model when two antennas of different polarities are used on the transmitter side, two antennas of different polarities are used on the receiver side, and the inclination of one of the receive antennas to one of the transmit antennas is equal to the inclination of the other one of the receive antennas to the other one of the transmit antennas.
Non-patent document 4 is a report on the past research in which one of the inventors of the present invention participated, and discloses an invention which performs unitary space-time modulation and demodulation and generates signals with a time lag provided therebetween using multiple antennas.
Further, non-patent documents 5 and 6 disclose coding and decoding schemes using Alamouti codes that are widely used in the STBC scheme.
The invention has been made to solve various problems of the known systems, and it is an object of the invention to provide a communication system, a transmitter, a receiver, a transmitting method, and a receiving method, which efficiently perform communications using antennas of different polarizations, and a program which allows a computer to realize them.